"Over the past few years, the visibility of a dangerous type of attack known as "zero-day" has increased. So has the confusion around what exactly constitutes such an attack. Fueled by the growing concerns of network security managers, vendors claim they are working rapidly to address the threat. But the prevalence of these attacks and the enormity of the damage they can cause are grossly underestimated. The key to combating the danger of zero-day attacks is to fully comprehend what they are, how they occur and what efforts are under way to stop them."
Complete article in http://www.securitypark.co.uk/article.asp?articleid=23438&CategoryID=1